Shuffling is triggered when your block can’t otherwise be completed using your specific bid preferences. This is a last step before Denial Mode.

Shuffling looks for different combinations of pairings that satisfy Award Pairings preferences located below the last negative bid preference (Prefer Off or Avoid Pairings preference). The goal is to complete the block without having to deny any (or additional)  bid preferences. The result is that crewmembers are  awarded pairings that match their Award Pairings preferences, but not pairings that necessarily match their highest Award Pairings preferences. The result is a complete block with the understanding that ultimately their higher priority bid preferences were honored and as a result.

Pairings awarded by Followed By bid preferences are not shuffled.

Armed with this knowledge, you may want to consider the  order in which your Award Pairings and Avoid Pairings bid preferences appear in your  bid, because shuffling only looks at the pairings awarded by the Award  Pairings preferences that come after the last deniable bid preference.

For example:

 

If your line is not complete after processing  the  system-generated Award Pairings lines, the N-PBS Scheduler would try to  exchange pairings awarded by bid preference 4 with pairings that could  be awarded by bid preference 5 in order to avoid having to deny bid preference 3. 

But if the bid was:

The N-PBS Scheduler would try to exchange any pairings  on the block, if necessary to avoid denying bid preference 2, because  all of the Award Pairings bid preferences come after the last Avoid Pairings  bid preference, which is line 2.

And if the bid was:

 

The N-PBS Scheduler would still try to shuffle, but only  within the Award Pairings (it is the only positive bid preference) bid  preference in order to avoid denying bid preference 5. If your line was  still not complete after denying bid preference 5, the N-PBS Scheduler  would attempt to exchange any pairings on the line from bid preference  2, 3, and 4, in order to avoid denying bid preference 1.

Once a bid preference is denied, the N-PBS Scheduler can shuffle Award Pairings bid preference above the denied preference, but not above the remaining negative bid preference(s).

If the bid was:

Bid preference 6 has been denied in the previous completion  attempt; in the subsequent completion attempt the N-PBS Scheduler could  shuffle, if necessary, using lines 4,5,and 7.

Pairings  awarded by Followed By bid preferences are not shuffled.